\chapter{Applications}

There are two claimed applications according to the discussed technical report which can be very much purposeful in providing data over an un-trustworthy channel. 

\section{Automatic Recovery from Structural Error} 
Structural Authentication Scheme is based upon structural ordering which makes it possible to recover from structural errors. Randomized order numbers are the backbone of this application. From these structural position (RPONs and RRONs), the original structure can be reconstructed. The cost of construction such a tree with $\mathit{V}$ vertices is $\mathit{O}$($\mid$$\mathit{V}$$\mid$ ). This facility helps automatic correction of data without the involvement of distributor.
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For instance a subtree is shared that contains two nodes ‘a’ and ‘b’. If their structural positioning is altered then this can be detected by using structural positioning scheme. Suppose ‘a’ is at right of ‘b’ but in-fact it was on the left. The user tests it using structural positions if the test succeeds the positions will be corrected. Likewise for a tree with vertices $\mathit{V}$ the reconstruction algorithm will be applied to obtain the non-contaminated tree.

\section{Secure Publish/ Subscribe of XML}
Publish-subscribe model can be efficiently used for the broadcasting of XML based data basically organized as tree structures. Structure based routing \cite{kundu2008new} was an old technique used to publish an XML document. They used encrypted post-order numbers for this purpose. Encrypted post-order numbers are in a way similar to RPONs but the method to publish was insecure. In this technique data distributors select and route the subtree based on this encrypted post-order number of the root of each subtree in the tree. This encrypted post-order number was used as routing parameter. The subscriber then uses these numbers to validate the veracity of the document but nothing could be said about the authenticity of data. As authenticity is a bigger security issue than integrity so this scheme was futile in secure routing of the XML document. It is also defenseless for attacks as post-order number single-handedly cannot inimitably characterize a tree's identity; hence if document is modified along the communication channel then this cannot be identified by the integrity verification process.
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Our considered report claims that Structural Authentication Scheme can deployed for secure publish and subscribe of an XML document. This involves 3 steps:
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\begin{description}[font=\normalfont\itshape\textbullet\space]
\item Sign an XML document using the claimed and proved signing scheme in the report.
\item Use RRONs or RPONs for enumeration as routing parameter.
\item Subscribe will receive this unique signature and will verify the integrity of the document using this structural signature. This is a sharp contrast of this technique with the previously described technique \cite{kundu2008new}, as in that a separate signature was received for each node.
\item In case of a revision of the XML document, only new signature of the updated document and the updated portion will be sent to the subscribers who are using the dynamic tree scheme.
\end{description}
	
Structural Authentication Scheme is not only secure but also more efficient as only one signature is sent and verified for integrity check.

